Bio-reactor design and operation is a complex engineering task. Under optimum conditions, cultivated stem cells and living cells must be able to perform their desired production with a 100 percent rate of success. The bio-reactor's environmental conditions, like gas content (i.e., air, oxygen, nitrogen and carbon dioxide), flow rates, temperature, pH and agitation speed/circulation rate need to be closely monitored and controlled.
A bio-reactor is a suitable device for cultivating stem cells or living cells or micro organisms being adherent and semi-adherent dependent or in suspension. Ideally, any stem cell or living cell or micro organism cultivating bio-reactor must maintain sterile conditions. In the aerobic process, optimal oxygen transfer and access is perhaps the most difficult task to accomplish. Oxygen is poorly soluble in water at atmospheric pressure, even less in cultivation broths, usually helped by agitation, which is also needed to mix nutrients and to keep the production homogeneous. There are, however, limits to the speed of agitation in stirred tank bio-reactors, due both to high power consumption and damages to the cultivated stem cells or living cells or micro organisms.
In bio-reactors the goal is to cultivate stem cells or living cells or micro organisms for mass production of stem cells or living cells for medical application, as regenerative medicine and therapeutic applications or drugs or more traditional expression from living cells or micro organisms of molecules for therapeutic purposes or as drugs.